Capacitor discharge ignition system with controlled spark duration

ABSTRACT

A capacitor discharge ignition system for a spark-ignition internal combustion engine. The ignition system includes an ignition coil having first and second primary windings, a secondary winding and a ferromagnetic core about which the windings are wound. A spark plug has electrodes which are spaced apart to form a spark gap which is connected in series with a first capacitor. The series-connected spark gap and first capacitor are connected across the secondary winding. A second capacitor is coupled to the first winding and a DC source of electrical energy is provided. First circuit means charge the second capacitor from the DC source and discharge this capacitor through the first primary winding in timed relation to operation of the engine. Second circuit means are provided for producing a fixed frequency oscillatory current in the second primary winding for a predetermined time interval subsequent to each discharge of the second capacitor through the first primary winding. The discharge of the second capacitor through the first primary winding and the subsequent supply of fixed frequency oscillatory current to the second primary winding causes ferroresonant oscillations in the secondary circuit of the ignition coil for at least a portion of the aforementioned predetermined time interval. The spark which occurs between the spark plug electrodes exists during the predetermined time interval and has a duration which may be varied as desired.

Asik et al.

[ Sept. 23, 1975 CAPACITOR DISCHARGE IGNITION SYSTEM WITH CONTROLLEDSPARK DURATION lnventorsz. Joseph R. Asik, Bloomfield Hills;

Mitsugu Hanabusa, Ann Arbor, both of Mich.

Ford Motor Company, Dearborn, Mich.

Filed: Apr. 24, 1974 App]. No.: 463,692

Assignee:

U.S. Cl 123/148 E; 315/209 CD Int. Cl. F02p 3/06 Field of Search 123/148E, 148 OCD;

References Cited UNITED STATES PATENTS Primary Examiner-Charles J. MyhreAssis tam Examiner.l0seph Cangelosi Attorney, Agent, or Firm-Robert W.Brown; Keith L. Zerschling ABSTRACT A capacitor discharge ignitionsystem for a sparkignition internal combustion engine. The ignitionsystem includes an ignition coil having first and second primarywindings, a secondary winding and a ferromagnetic core about which thewindings are wound. A spark plug has electrodes which are spaced apartto form a spark gap which is connected in series with a first capacitor.The series-connected spark gap and first capacitor are connected acrossthe secondary winding. A second capacitor is coupled to the firstwinding and a DC source of electrical energy is provided. First circuitmeans charge the second capacitor from the DC source and discharge thiscapacitor through the first primary winding in timed relation tooperation of the engine. Second circuit means are provided for producinga fixed frequency oscillatory current in the second primary winding fora predetermined time interval subsequent to each discharge of the secondcapacitor through the first primary winding. The discharge of the secondcapacitor through the first primary winding and the subsequent supply offixed frequency oscillatory current to the second primary winding causesferroresonant oscillations in the secondary circuit of the ignition coilfor at least a portion of the aforementioned predetermined timeinterval. The spark which occurs between the spark plug electrodesexists during the predetermined time interval and has a duration whichmay be varied as desired.

9 Claims, 17 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of43,906,919

I v E Q EN IIIIIIIL Sept. 23,1975 Sheet 2 of 4 3,906,919

US Patent D HM US Patent Sept. 23,1975

Sheet 3 of 4 CAPACITOR DISCHARGE IGNITION SYSTEM WITH CONTROLLED SPARKDURATION BACKGROUND This invention relates to a capacitor dischargeignition system for a spark-ignition internal combustion en gine. Moreparticularly. it relates to a ferroresonant capacitor discharge ignitionsystem which produces a spark discharge in the gap of a spark plug. Thespark discharge is of controllable duration and is characterized byalternating current flow in the spark gap and a sustained alternatingvoltage in the secondary circuit of an ignition coil. This voltageoscillates at a ferroresonant frequency. The present invention isrelated to our commonly assigned patent application Ser. No. 463,919filed Apr. 24, 1974 and entitled Ferroresonant Capacitor DischargeIgnition System.

Our copending patent application identified above relates to a capacitordischarge ignition system which has an ignition coil with a primarywinding and a secondary winding wound about a ferromagnetic core. Thesystem includes a spark gap which is connected in series with a firstcapacitor. The series-connected first capacitor and spark gap areconnected across the ignition coil secondary winding and a secondcapacitor is coupled to the ignition coil primary winding and to a DCsource of electrical energy. Circuit means are provided for charging thesecond capacitor and for discharging it through the primary winding intimed relation to engine operation. This produces breakdown of the sparkgap in the secondary circuit and subsequent oscillations in thiscircuit. The secondary circuit oscillations are at a frequency f definedby the expression f= V,,,/4N 12 where V, is the instantaneous maximumvoltage across the first capacitor. N is the number of turns in thesecondary winding of the ignition coil and D is the magnetic fluxenclosed by the secondary winding of the ignition coil at saturation ofits ferromagnetic core.

The present invention is an improvement over the capacitor dischargeignition system described above in that it provides an ignition systemwhich operates in a ferroresonant mode as defined by the aboveexpression, but which also provides sustained and controllable sparkduration characterized by ferroresonant oscillations in the secondarycircuit of the ignition coil.

SUMMARY OF THE INVENTION It is an object of the invention to provide acapacitor discharge ignition system which has controllable sparkduration.

Another object of the invention is to provide an ignition system whichis characterized by sustained oscillation in the secondary circuit of anignition coil at ferroresonant frequencyf= V,,,/4N I A further object ofthe invention is to provide an ignition system that causes analternating current to flow through the gap of a spark plug.

A still further object of the invention is to provide an ignition systemwhich causes a spark discharge or breakdown in the gap -of a spark plugsubsequent to which the spark is sustained and ferroresonantoscillations occur in the secondary circuit of the ignition coil for apredetermined time interval.

Still another object of the invention is to provide an ignition systemhaving restrike capability such that multiple sparks of sustainedduration may be produced within the gap of the spark plug during onecombustion cycle in a combustion chamber of an internal combustionengine.

A capacitor discharge ignition system in accordance with the inventioncomprises an ignition coil having first and second primary windings, asecondary winding and a ferromagnetic core about which the windings arewound. A spark plug has electrodes spaced to form a spark gap. One ofthe electrodes is coupled to one terminal of the secondary winding andthe spark gap is connected in series with the first capacitor. Oneterminal of the capacitor is coupled to the other terminal of thesecondary winding. A second capacitor is coupled to the first primarywinding and a DC source of electrical energy is provided.

First circuit means are coupled to the second capacitor and to the firstprimary winding. The first circuit means controls the charging of thesecond capacitor from the DC source of electrical energy and controlsits discharge through the first primary winding in timed relation tooperation of the engine. Second circuit means, coupled to the secondprimary winding. are provided for producing a fixed frequencyoscillatory current in the second primary winding for a predeterminedtime interval subsequent to each discharge of the second capacitorthrough the first primary winding. The discharge of the second capacitorthrough the first primary winding and the subsequent supply of the fixedfrequency oscillatory current to the second primary winding produces,for at least a portion of the predetermined time interval, a voltage inthe secondary circuit of the ignition coil which oscillates at a fixedfrequency f defined by the expression f= V,,/4N I where V,,, is theinstantaneous maximum voltage across the first capacitor, N. is thenumber of turns in the secondary winding and ID is the magnetic fluxwithin the secondary winding when the core of the ignition coil ismagnetically saturated.

The invention may be better understood by reference to the detaileddescription which follows and to th drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. la and lb together form acomplete schematic diagram of a capacitor discharge ignition system inaccordance with the invention;

FIGS. 2 through 13 are reproductions of actual voltage and currentwaveforms observed on an oscilloscope; these waveforms have the sametime base and illustrate the phase relationships of signals which occurat various points in the circuit shown schematically in FIGS. la and lb.

DETAILED DESCRIPTION With reference now to the drawings, wherein likenumerals refer to like parts in the several views, there is shown inFIGS. la and 1b a complete schematic diagram of a capacitor dischargeignition system capable of operation in a ferroresonant mode inaccordance with the invention. Various portions of the electricalcircuit are enclosed by broken lines and given designations with respectto their function in the circuit. The complete ignition circuit of FIGS.la and 1b is designated by the numeral 10.

In FIG. In, it may be seen that the ignition system 10 includes anignition coil 12 which has a first primary winding P1, a second primarywinding P2 and a secondary winding 5. The ignition coil 12 has aferromagnetic core 14 which in the circuit is capable of being saturatedrepetitively after the initial breakdown of a spark gap 26. Morespecifically, the secondary winding 5 of the ignition coil has one ofits leads connected to one terminal of a capacitor C1. The otherterminal of the capacitor C1 is connected to ground at 16. A lead 18extends from the other terminal of the secondary winding S to the rotor20 of a conventional distributor 22 for a sparkignition internalcombustion engine. The distributor 22 has eight contacts 24 which arerepetitively and serially contacted by the rotor 20 such that repetitiveelectrical contact is made with the eight spark gaps 26 contained in thespark plugs of the internal combustion engine. Thus, each of the sparkplugs has one of its electrodes, represented by a lead 25, connected tothe secondary winding S of the ignition coil and has its other electrode27 connected to ground at 28. It should be noted that the groundconnections 16 and 28 are common and, therefore, each of the spark gaps26 is connected, sequentially as the rotor 20 rotates, in series withthe capacitor C1. The capacitor C1 need not be located as shown in FIG.1, but rather may be connected in series with the spark gap 26, forexample, by its insertion in the lead 18, the lead or the lead 27. 1fthe capacitor C1 is inserted in the leads 25 or 27, a separate capacitoris required for each spark gap. Similarly, a separate secondary windingS may be provided for each of the spark gaps 26 if desired. Separatesecondary windings S and capacitors C1 for each of the spark gaps 26 maybe housed within the spark plug, for example, as depicted in the sparkplug design of US Pat. No. 3,267,325 issued Aug. 16, 1966 to J. F. Why.

The first primary winding P1 of the ignition coil 12 has one of itsterminals connected to ground at 30 and has its other terminal 32coupled, through a saturable, ferromagnetic core inductor L2 and a lead34, to a capacitor C2. The capacitor C2 is connected to ajunction 36formed between a resistor R1 and the anode of a semiconductor controlledrectifier (SCR) Q7. The cathode of the SCR is connected to ground. TheSCR has a gate or control electrode 38. The current limiting resistor R1is connected through another saturable, ferromagnetic core inductor L1to a +350 volt DC source of electrical energy. This voltage, as well asthe other Dc voltages shown in FIG. 1, may be obtained from a 12 volt DCsource of electrical energy, such as the storage battery 44 conventionalin motor vehicles, through use of a DC to DC converter well known tothose skilled in the art.

An input matching circuit, a duration gate generator, a restrikeoscillator, an SCR driver and an SCR switch comprise circuit means forcharging the capacitor C2 from the DC source of electrical energy andfor discharging this capacitor through the first primary winding P1 intimed relation to operation of the engine. The charging and dischargingof the capacitor C2 in timed relation to the engine operation may beobtained in the conventional manner by a cam 40 mechanically coupled tothe distributor rotor 20, driven by the engine, and used tointermittently open and close a set of breaker points 42, one of whichis connected to ground and the other of which is connected at a junction46. Because the DC source of electrical energy 44 has its negativeterminal corrected to ground has has its positive terminal connectedthrough a resistor R2 to the junction 46, the junction 46 is at groundpotential when the breaker points 42 are closed and is at the +12 voltpotential of the storage battery 44 when the breaker points are open.The voltage rise at the junction 46 which occurs each time the breakerpoints open is supplied to an input matching circuit to cause theproduction of a spark in one of the spark gaps 26.

As indicated above, the circuitry 10 includes an input matching circuit.The function of this circuit is to couple the pulses occurring at thejunction 46 to a duration gate generator. The duration gate generatorproduces a pulse output signal which has a controllable duration andwhich is supplied to the restrike oscillator. The function of therestrike oscillator is to produce one or more pulse signals during theduration of the signal from the duration gate generator. Each pulseproduced at the output of the restrike oscillator is used to initiatethe discharge of the capacitor C2 through the ignition coil firstprimary winding P1. The output pulses from the restrike oscillatorcircuit are supplied to an SCR driver circuit which utilizes therestrike oscillator pulses to produce pulse spikes which are applied tothe gate 38 of the SCR Q7. An interlock circuit is provided to prevent,when the ignition circuit 10 is first put into operation, the supply ofa pulse to the gate electrode 38 until the capacitor C2 has hadsufficient time to charge. In the paragraphs which follow, the abovecircuit portions are described in detail.

The input matching circuit includes a choke inductor L3 which has one ofits terminals connected to the junction 46 and which has its otherterminal connected to the cathode of a zener diode D1. The anode of thiszener diode is coupled to ground through a resistor R3 connected inparallel with a noise suppression capacitor C3. The anode of the zenerdiode also is connected through the series combination of a DC blockingcapacitor C4 and a current limiting R5 to the base of an NPN transistorQ1. The junction formed between the capacitor C4 and the resistor R5 isconnected to the cathode of a zener diode D2 whose anode is connected toground. A resistor R4 is connected in parallel with the zener diode D2.The emitter of the transistor Q1 also is connected to ground and itscollector is connected through resistors R6 and R7 to a +18 volt DCsupply lead 48.

The function of the resistor R3 and capacitor C3 is to suppress highfrequency noise signals that may appear at the anode of the zener diodeD1. The capacitor C4 permits the positive step voltage, which occurs atthe junction 46 when the breaker points 42 open, to momentarily passthrough the resistor R5 to the base of the transistor O1 to render itmomentarily conductive in its collector-emitter output circuit. Thispermits current to flow through the resistors R7 and R6 to ground.

The duration gate generator has a blocking capacitor C5 connected to thejunction formed between the resistors R6 and R7. The opposite terminalof the capacitor C5 is connected through a current limiting resistor R9to the base of a PNP transistor Q2. The junction formed between thecapacitor C5 and the resistor R9 is connected through a resistor R8 tothe voltage supply lead 48. The emitter of the transistor Q2 also isconnected to the supply lead 48 and its collector is connected throughseries-connected resistors R10, R11 and R12 to a 18 volt DC supply lead50. The resistor R12 is variable and controls the duration (total lengthof time) of multiple spark discharges produced in a given spark gap 26during one combustion cycle in the engine. More specifically theresistor R12 controls the duration of the output signal pulse from theduration gate generator. in a reciprocating spark-ignition internalcombustion engine. the length or duration of this output pulse is thelength of time available for the production of one or more sparks in thespark gap 26 in a given cylinder to cause ignition of a combustiblemixture of fuel and air and a resultant power stroke of the piston inthat cylinder.

The capacitor C6 has one of its terminals connected to the voltagesupply lead 48 and has its other terminal connected to thejunctionformed between the resistors R and R11. Also connected to this junctionis the cathode of a clamping diode D9 which has its anode connected toground. The diode D9 limits the negative voltage at thisjunction to onediode voltage drop below ground potential. The junction formed betweenthe resistors R10 and R11 also is connected through a coupling capacitorC7 and a current limiting resistor R to the base of a PNP transistor Q3.The junction formed between the capacitor C7 and resistor R15 isconnected through a resistor R13 to the negative voltage supply lead 50.The collector of the transistor Q3 also is connected through a resistorR15 to the supply lead 50, and the emitter of this transistor isconnected to the positive voltage supply lead 48. The collector of thetransistor O3 is connected through a resistor R16 to the base of an NPNtransistor Q4 Whose emitter is connected to ground. A clamping diode D3has its cathode connected to the base of the transistor Q4 and has itsanode connected to ground to limit the base voltage to one diode voltagedrop below ground potential. The output signal of the duration gategenerator is taken at the collector of the transistor Q4 which is connected to pin 7 of a dual monostable multivibrator U1, which as shown isa Teledyne type 342. A Texas Instruments type 15342 or the equivalentalso may be used for U1.

The duration gate generator is a sawtooth generator which is triggeredwhen the transistor Q1 is rendered conductive, which occurs, aspreviously stated, when the breaker points 42 open. When the transistorQ1 is rendered conductive, the resistor R8 and capacitor C5differentiate the resulting negative voltage step at the collector ofQ1. The negative voltage spike which results is applied to the base ofthe transistor Q2. This renders the transistor Q2 conductive in itsemittercollector output circuit for a time sufficient to permit thedischarge of the capacitor C6 through the resistor R10 and theemitter-collector circuit of the transistor Q2. The capacitor C6 willhave previously been charged to a voltage slightly in excess of 18 voltsDC. The transistor O3 is normally conductive in its emittercollcctoroutput circuit due to the flow of current from the voltage supply lead48, through its emitter-base junction. through the resistor R15, andprimarily through the resistor R13 to the negative voltage supply lead50. However, when the capacitor C6 discharges, a positive voltageapproximately equal to the voltage on the supply lead 48 appears at thejunction formed between resistors R10 and R11. This voltage is appliedthrough the capacitor C7 and the resistor R15 to the base of thetransistor O3 to render it nonconductive. The transistor Q3 remainsnonconductive for the length of time required for the capacitor C6,after the transistor Q2 again becomes nonconductive, to recharge throughthe series resistors R11 and R12. Typically, the transistor Q3 isnonconductive for a time period of from 1 to 5 ms. When the transistorQ3 is rendered nonconductive and for so long as it is nonconductive, thetransistor Q4 has no base drive and also is nonconductive which resultsin the application of a positive voltage at the pin 7 of the dualmonostable multivibrator U1.

The dual monostable multivibrator U1 has one monostable multivibratorwith an input A and an output 6,. The other monostable multivibrator inthe integrated circuit Ul has an input A and an output Q By theconnection of the Q, output to the A input and the connection of the Qoutput to the A input, as is accomplished by the connection of the lead52 between the pins 5 and 10 and the connection of the pins 6 and 11 ata junction 54, the dual monostable multivibrator U1 becomes a pulsegenerator, the output of which is taken at its pin 2. The O output atpin 2 alternates between a high voltage level of about 10 volts and alow voltage level near ground potential. With the circuit valuesindicated in the drawings, the high voltage portion of the signal at pin2 is approximately 68 percent of the signal period. Dual variableresitors R18 and R19 are connected, respectively, through a resistor R20and a capacitor C9 to the pins 3 and 4 and through a resistor R21 and acapacitor C10 to the pins 12 and 13. These components determine the dutycycle or pulse width at output pin 2 of the multivibrator and permit theperiod of the signal at pin 2 to be varied from about 0.30 ms to 1.5 ms.The period of the signal at pin 2 rep resents the restrike delay, thatis, the delay between multiple ignition sparks produced in each of thespark gaps 26 by repetitive triggering of the SCR Q7.

The dual monostable multivibrator U1 is triggered or gated when theoutput circuit of the transistor O4 is rendered nonconductive. When thetransistor Q4 is conductive, the signal at pin 2 of the dual monostablemultivibrator U1 remains constant at a low voltage level, but when thetransistor Q4 becomes nonconductive, gating multivibrator U1, the signalat pin 2 becomes a series of pulses which continually gate the SCR O7 toproduce a spark in a spark gap 26 each time a pulse occurs at pin 2.These repetitive and restriking sparks continue to occur until thetransistor Q4 is once again rendered conductive.

The dual monostable multivibrator U1 receives its positive voltagesupply from a voltage regulator comprising a resistor R17 connected inseries with the parallel combination of a zener diode D4 and a capacitorC8. The junction formed between these components is connected to thevoltage supply pin 16 of U1 and also is connected to the variableresistors R18 and R19. Pin 8 of the multivibrator U1 is connected toground. Pin 2 of the multivibrator is connected through a currentlimiting resistor R22 and azene-r diode D5 to the base of an NPNtransistor Q5. 1

The transistor Q5 is located in the SC R driver portion of the circuit10 and has its emitter connected to ground. Its collector is connectedthrough a resistor R27 to the voltage supply lead 48 and also isconnected through a current limiting resistor R28 to the base of PNPtransistor Q6. The emitter of the transistor Q6 is connected to thevoltage supply lead 48 and its collector is connected through a resistorR29 and a lead to a -18 volt DC voltage supply. The collector of thetransistor Q6 also is connected, through a series circuit includingdifferentiating capacitor C12, resistor R30 and zener diode D8, to thegate electrode 38 of the SCR Q7.

The waveforms shown in FIGS. 2 through 13 are representations of signalswhich occur at various points in the circuit schematically illustratedin FIG. 1, with the exception that the waveforms 11, I2 and I3 pertainto a 35 mil spark gap located in air at atmospheric pressure rather thanto a spark gap located in the cylinder of an operating internalcombustion engine.

FIG. 2 shows the voltage waveform that occurs at pin 2 of the dualmonostable multivibrator Ul. This voltage is the oscillatory outputvoltage of the multivibrator which occurs so long as the inputtransistor Q4 connected to its pin 7 is in a nonconductive state. Ofcourse, Q4 is rendered nonconductive each time, and for a predeterminedtime established by the duration gate generator, that the cam 40 opensthe breaker points 42. On each positive going edge of the pulses in FIG.2, the transistor Q5 is rendered conductive. This reduces its collectorvoltage to substantially ground potential to cause the conduction of thePNP transistor Q6. When nonconductive, the collector of the transistorQ6 is at approximately 18 volts DC, but when rendered conductive, itscollector achieves a voltage of almost +18 volts DC. This step voltageon the collector of the transistor Q6 is differentiated by the capacitorC12 to produce a voltage spike which gates the SCR Q7. The voltagespikes are represented in FIG. 6, which illustrates the voltage spikesoccurring on the resistor R30 at points corresponding to the positivegoing edges of the pulses of FIG. 2, which pulses occur at pin 2 of themultivibrator. Thus, it is apparent that the SCR O7 is gated ortriggered on each positive going edge of the oscillatory signaloccurring at pin 2 of the multivibrator U1 and that this continues solong as the transistor Q4 is nonconductive. If the duration gategenerator is adjusted such that the transistor Q4 is nonconductive for 5milliseconds and if the restrike delay resistor R18 and R19 are adjustedsuch that the signal of FIG. 2 has a period of 0.33 ms, then the gate 38of the SCR Q7 will receive 16 trigger pulses during the course of the 5ms that the transistor Q4 is nonconductive. This produces acorresponding 16 spark discharge in a single one of the spark gaps 26.It should be noted that 5 ms is ap proximately the time required for thepiston in an eightcylinder, four-cycle reciprocating internal combustionengine to travel from its topdead-center positin to itsbottom-dead-center position when the engine is operating at 6,000 rpm.

With respect to the interlock portion of the circuitry 10, it may beseen that this circuit portion comprises NPN transistors Q8 and Q9. Theemitters of these transitors are connected to ground potential. Thecollector of the transistor O9 is connected. through a diode D6, to thejunction formed between the resistor R22 and the zener diode D5. Thecollector of this transistor also is connected through a resistor 23 toa lead 57 connected to a +18 volt DC source of electrical energy. Acurrent limiting resistor R25 is connected between the lead 57 and thecollector of the transistor Q8. The collector of the transistor Q8 alsois connected through a current limiting resistor R25 to the base of thetransistor Q9. A seriesconnected resistor R26 and capacitor C11 areconnected between the lead 57 and ground potential. The junction formedbetween the resistor R26 and the capacitor C11 is connected through azener diode D7 to the base ,of the transistor Q8. Upon the initialapplication of the DC supply potential to the lead 57, the transistor Q9immediately is conductive in its collector-emitter output circuit. Thishas the effect of connecting connecting the pin 2 output of themultivibrator U1 to ground potential to prevent the conduction of thetransistor Q5 and, consequently, to prevent the supply of a triggeringQ5 and, consequently, to prevent the supply of a triggering pulse to thegate electrode 38 of the SCR Q7. At this time, the transistor Q8 isnonconductive in its output circuit because the capacitor C11 forms aneffective short circuit of its baseemitter circuit. However, thecontinued application of the DC voltage on the lead 57 causes thecapacitor C1 1 to be charged through the resistor R26.

When the voltage on the upper terminal of the capacitor C11 exceeds thesum of the breakdown voltage of the zener diode D7 and the base-emittervoltage drop required to render the transistor Q8 conductive, then thecollector-emitter circuit of transistor Q8 becomes conductive and shuntsthe base-emitter circuit of the transistor Q9. The transistor Q9 thenbecomes nonconductive and the positive going edges of the oscillatorysignal at pin 2 of the multivibrator U1 are permitted to cause therepetitive triggering of the gate electrode 38 of the SCR Q7. The timerequired to charge the capacitor C11 exceeds considerably the timerequired to charge the capacitor C2 connected to the first primarywinding P1 of the ignition coil 12. The capacitor C2 must be fullycharged before the SCR Q7 is triggered because the latter isself-commutated as a result of the discharge of the capacitor C2 throughit and the first primary winding P1. Of course, the interlock circuitryshown in FIG. 1a may be replaced by gate circuitry which prevents theapplication of a trigger signal on the gate electrode 38 of the SCRprior to the required charge level on the capacitor C2 being attained.

When the SCR Q7 is nonconductive between its anode and cathode, thecapacitor C2 is charged from the +350 volt DC power suply through thecurrent path including the inductor LI, the resistor R1, the inductorL2, the first primary winding P1 of the ignition coil 12 and the groundcircuit. When the SCR Q7 is triggered by a positive pulse applied to itsgate electrode 38, a current spike is produced. Two such current spikes,caused by two successive trigger pulses applied to the gate electrode 38are shown in waveform of FIG. 9. It may be seen that these currentspikes have an alternating current waveform. At the end of the spike,the SCR Q7 is self-commutated. This self-commutation is aided by thesaturable inductor L2 which offers little impedance to current flow dueto its saturable character.

FIG. 10 shows the voltage across the first primary winding Pl upon theoccurrence of the current spikes shown in FIG. 9. It may be seen thatthis voltage is oscillatory, that it has a voltage spike corresponds tothe breakdown of one of the spark gaps 26, and that the amplitude issubstantially constant for the time interval during which current flowsthrough the spark gap (this current is shown in FIG. 11 hereinafterdescribed).

The sustain oscillator. the sustain gate, the sustain driver and thesustain power amplifier generally comprise circuit means for producing afixed frequency 05- cillatory current in the second primary winding P2for a predetermined time interval subsequent to each discharge of thecapacitor C2 through the first primary winding P1. The sustain gate istriggered by a signal which triggers the SCR Q7 and producesoscillations of a square-wave character and of fixed frequency. Theseoscillations receive current and power amplification through the sustaindriver and sustain power amplifier circuits, and the amplifiedoscillatory currents flow through the second primary winding P2 of theignition coil 12.

The sustain oscillator includes a dual monostable multivibratorintegrated circuit U2. The dual monostable multivibrator U2 as shown hasthe pin connections of a Motorola Semiconductor Corporation type MC 667,but equivalent devices may be substituted. Dual monostable multivibratorU2 has its Q output connected to its T input and has its Q outputconnected to its T input. Thus, lead 64 interconnects pins 1 and 8 of U2and pins 6 and 13 are interconnected at ajunction 66 which forms thetrigger input to the multivibrator U2. The trigger input is supplied viaa lead 68 connected to the collector of a transistor Q11. The emitter ofthe transistor Q11 is connected to ground.

A lead 62 is connected to the junction 54 connected to pins 6 and 11 ofthe dual monostable multivibrator U1 in the restrike oscillator. Thesignal on these pins is the same as the pin 2 signal shown in FIG. 2.Lead 62 is connected through a resistor R31 to the cathode of zenerdiode D10, the anode of which is connected to the base of NPN transistorQ10. The emitter of the transistor Q is connected to ground and itscollector is connected through a current limiting resistor R33 to a +18volt DC source of electrical energy. A resistor R32 is connected to thissource and to the junction formed between the resistor R31 and thecathode of the zener diode D10. The collector of the transistor Q10 alsois connected through a current limiting resistor R34 to the base of anNPN transistor Q11. When the voltage on the lead 62 is at its highvoltage level, the transistor Q10 is conductive in its output circuitand its collector voltage is substantially at ground potential. Thisrenders the transistor Q11 nonconductive in its output circuit and itscollector is isolated from ground potential. On the other hand, when thesignal on the lead 62 is a low voltage, the transistor Q10 isnonconductive, which causes the transistor Qll to be conduc tive in itscollector-emitter output circuit and results in the connection of thepins 6 and 13 of the dual monostable multivibrator U2 to substantiallyground potential.

The dual monostable multivibrator U2 is connected as a square-waveoscillator which has a duty cycle and period determined by theparallel-connected resistors R35 and R36 connected across pins 10 and 11and the capacitor C13 connected between pins 9 and l 1 and by theparallel-conected resistors R37 and R38 connected across pins 3 and 4and the capacitor C14 connected between the pins 3 and 5. Resistors R36and R37 are variable to provide an oscillator output signal on the Qoutput at pin 2 of the multivibrator U2 which has a fre quency variablebetween 17 KHZ and 35.7 KI-Iz. The output on the pin 2 of the dualmonostable multivibrator U2 is a low level voltage whenever the voltageon pin 2 of the dual monostable multivibrator U1 is a low voltage, andthe voltage on pin 2 of the dual monostable multivibrator U2 isoscillatory between 12 volts and ground potential whenever the voltageon pin 2 of the dual monostable multivibrator U1 is at a high voltagelevel. The oscillatory voltage at pin 2 of the multivibrator U2 isapplied through a current limiting resistor R40 to the base of an NPNtransistor Q12. The emitter of the transistor Q12 is connected to groundand its collector is connected through a current limiting resistor R41to a lead 58 connected to a+18 volt DC source of electrical energy. Thevoltage supply to the multivibrator U2 is obtained from a resistor R39connected to the lead 48 and to the parallel combination of a filtercapacitor C15 and a zener diode D11 which are con nected between the pin14 of U2 and ground potential. This provides a regulated supply voltagefor multivibrator U2. Pin 7 of the multivibrator U2 is connected to aground lead 70.

The output signal of the sustain oscillator is obtained on a lead 72connected to the collector of the transistor Q12. This signal is shownin FIG. 4 where it may be seen that the voltage oscillates between about+18 volts DC and 0 volts DC. Because each of the high voltagelevelpulses at pin 2 of the multivibrator U1 results in a trigger signalbeing applied to the gate 38 of the SCR Q7, and from the waveform ofFIG. 4, it is clear that an oscillatory signal is produced on the lead72 of the sustain oscillator each time the SCR Q7 is triggered. Thisoscillatory signal has a duration corresponding to the duration of thehigh-voltage-level pulses shown in FIG. 2. These sustained oscillationson the lead 72 cause, in a manner hereinafter described, currentoscillations in the second primary winding P2 of the ignition coil 12.

With particular reference now to FIG. 11;, there is shown the sustaingate, the sustain driver and the sustain power amplifier, the functionsof which are to pro vide current and power amplification of theoscillatory signals occuring on the lead 72 which is connected through acurrent limiting resistor R48 to the base of PNP transistor Q15 in thesustain gate. The emitter of the transistor Q15 is connected to a +18volt DC supply lead 74 and its collector is connected through a currentlimiting resistor R49 to a -18 volt DC supply lead 76. The voltage onthe collector of the transistor Q5 in the SCR driver portion of thecircuitry is shown in FIG. 3 as the complement of the signal on pin 2 ofthe dual monostable multivibrator U1 and is supplied via a lead 59 andthrough a current limiting resistor R42 to the base of a PNP transistorQ13. The emitter of this transistor is connected to the voltage supplylead 74 and its collector through a resistor R43 to the negative voltagesupply lead 76. Its collector also is connected through a currentlimiting resistor R45 to the base of a PNP transistor Q14. The collectorof Q14 is connected through a current limiting resistor R46 to thenegative voltage supply lead 76 and its emitter is connected to thevoltage supply lead 74.

A diode gate is formed by diodes D12, D13, D14 and D15. The anodes ofthe diodes D12 and D13 are connected together and, through a resistorR44, are connected to the collector of the transistor Q13. The cathodeand anode junction formed between diodes D12 and D14 is connected by alead 78 to the collector of the transistor Q15 and the cathodes of thediodes D14 and D15 are connected, through a resistor R47, to thecollector of the transistor Q14. The junction formed between the cathodeof the diode D13 and the anode of the diode D15 is connected by a lead80, which is the output of the sustain gate, to one terminal of aresistor R50 the other terminal of which is connected to ground. Thelead also is connected through a resistor R51 to the base of an NPNtransistor Q16 and through a resistor R52 to the base of a PNPtransistor Q17. Transistors Q16 and Q17 form a push-pull amplitier andthus have their emitters connected together and to ground potential. Thecollector of the transistor Q16 is connected through a current limitingresistor R53 to the voltage supply lead 74, and the collector of thetransistor Q17 is connected through a resistor R54 to the negativevoltage supply lead 76. Also, the collector of the transistor Q16 isconnected to the base of a PNP transistor Q18 whose emitter is connectedto the voltage supply lead 74 and whose collector is connected via alead 82 and a resistor R55 to ground Similarly, the collector of thetransistor Q17 is connected to the base of NPN transistor Q19 whoseemitter is connected to the negative voltage supply lead 76 and whosecollector is connected to the lead 82 and, through the resistor R55 toground potential. It may be appreciated that when the transistor Q16 isconductive in its collector-emitter output circuit, the transistor Q18also is conductive to permit current flow from the voltage supply lead74 to the lead 82, and, through the resistor R55, to ground. Likewise,when the transistor Q17 is conductive in its emitter-collector outputcircuit, the output circuit of the transistor Q19 is conductive topermit current to flow from ground, through the resistor R55 and throughthe colector-emitter output circuit of the transistor Q19 to thenegative voltage supply lead 76.

As may be seen from FIGS. 3 and 4, prior to the occurrence ofoscillations on the lead 72, the voltage on this lead is at about +18volts, as is the voltage on the gate signal lead 59. Thus, theemitter-base junctions of the transistors Q15 and Q13 are reverse-biasedand these transistors are non-conductive. In such case, the voltage onthe sustain-gate output lead 80 is at ground potential. When the voltageat pin 2 of the dual monostable multivibrator U1 rises to about volts tocause the application of a trigger signal on the gate lead 38 of the SCRQ7, the gate signal on lead 59 falls to a few volts as shown in FIG. 3.At the same time, the voltage on the lead 72, connected to the collectorof the transistor Q12 in the sustain oscillator, oscillates betweenabout +18 volts DC and substantially ground potential as shown in FIG.4. The low voltage on the lead 59 renders the transistor Q13 conductive.This results in the application of about +18 volts to the base of thetransistor Q14 and it is rendered nonconductive in its output circuit.The oscillations on the lead 72 are applied through the resistor R48 tothe base of the transistor Q15 to render its emitter-collector outputcircuit conductive and nonconductive in a corresponding oscillatorymanner. Thus, the lead 78 alternates between +18 volts and 18 volts.When the lead 78 is at +18 volts, current flows from the collector ofthe transistor Q13 through the resistor R44, through the diode D13 andinto the lead 80. At the junction formed between lead 80 and theresistor R50 the current divides, part of it flowing to ground throughthe resistor R50 and the remainder flowing through the resistor R51 andbaseemitterjunction of the transistor Q16 to ground. When the lead 80 isat l8 volts, currents flow from ground through the resistor R50 and fromground through the emitter-base junction of the transistor Q17 and theresistor R52 to the lead 80 where there currents are combined. Thecombined current flows from the lead 80, through the diode D15, theresistor R47 and the resistor R46 to the negative voltage supply lead76. Under such circumstances, the voltage waveform on the lead 80 is asshown in FIG. 5.

The transistors Q16 and Q17 are alternately conductive during theoscillatory voltage which occurs on the lead 72. These transistorsamplify the alternating voltage signal on the lead 80.

When the transistor Q16 is conductive on alternative half cycles, thetransistor Q18 also is conductive to provide current and poweramplifications. Similarly, when the transistor Q17 is conductive, thetransistor Q19 is also conductive to provide amplification. The voltageon the collectors of the transistors Q18 and Q19, during theoscillations on the lead 72, also oscillates between about +18 and 18volts. This alternating voltage, when positive, is applied through acurrent limiting resistor R56 to the base of a transistor Q20 to renderit conductive, and, when negative, is applied through a current limitingresistor R56 to the base of a transistor Q21 to render it conductive.The emitters of the transistor Q20 and Q21 are connected together and toground, the collector of the transistor Q20 is connected through aresistor R58 to the voltage supply lead 74, and the collector of thetransistor Q21 is connected through a resistor R59 to the voltage supplylead 76. The transistor Q20 and Q21 form a push-pull amplifier.

The collector of the transistor Q20 is connected through a currentlimiting resistor R60 to the base of a transistor Q22, the emitter ofwhich is connected through a resistor R62 to the voltage supply lead 74.The colector of the transistor Q21 is connected through a currentlimiting resistor R61 to the base of a transistor Q23 whose emitter isconnected through a resistor R63 to the voltage supply lead 76. Thecollectors of the transistors Q22 and Q23 are connected together. Adiode D16 has its cathode connected to the emitter of the transistor Q22and has its anode connected to the collector of this transistor.Similarly, a diode D17 has its cathode connected to the collector of thetransistor Q23 and has its anode connected to the emitter of thistransistor. Transistor Q22 is conductive when transistor Q20 isconductive, and transistor Q23 is conductive when transistor Q21 isconductive.

The junction formed between the collectors of the transistors Q22 andQ23 is connected by a lead 84 to the junction formed between a resistorR64 and a saturable inductor L4. The opposite terminalof the resistorR64 is connected to ground. Lead 19 connects the opposite terminal ofthe saturable inductor L4 to the second primary winding P2 of theignition coil 12 and the lead 21, connected to the opposite terminal ofthis second primary winding, is connected to ground. Thus, the resistorR64 is connected in parallel with the seriesconnected saturable inductorL4 and second primary winding P2. The alternating conduction of thetransistors Q22 and Q23 in response to the oscillations on the lead 72causes an alternating current to flow through the saturable inductor L4and the second primary winding P2 of the ignition coil to sustain aspark in the gap 26 of a spark plug for a time period determined by thelength of time the oscillation continues on the lead 72. The alternatingvoltage across and current flow through the second primary winding P2are shown, respectively, in FIGS. 7 and 8.

As was previously mentioned, FIG. 9 shows the current flow through theprimary winding PI for two spark discharges through a spark gap 26. Itmay be seen that two alternating current spikes occur, one for each ofthe SCR Q7 gate signal pulses which occur as shown in FIG. 6. These gatesignal pulses result in conduction of the SCR Q7 and the discharge ofthe capacitor C2 through the first primary winding P1. This breaks downa spark gap 26, causes ferroresonant oscillations to occur in thesecondary circuit of the ignition coil 12, and causes the sustain gate,sustain oscillator, and sustain amplifier circuitry to producealternating current in the second primary winding P2. The frequency ofthis alternating current is selected to sustain a ferroresonant mode ofoscillation in the ignition coil secondary circuit.

FIG. 11 depicts the current through a 35 mil spark gap, located in airat atmospheric pressure, for two spark discharges, each of which isinitiated by the discharge of the capacitor C2 through the first primarywinding P1 and each of which is sustained for a predetermined timeinterval as a result of the alternating current flow through the secondprimary winding P2. It may be seen that this current flow through thespark gap is alternating in direction, that the initial amplitude andfrequency, that is, for about the first 75 microsec onds of the sparkdischarge, is higher than the fixed fre quency and amplitude of currentflow which occurs thereafter, and that the alternating current flowthrough the spark gap is nonsinusoidal, which is the result offerroresonent oscillation in the secondary circuit of the ignition coil12, this ferroresonent oscillation resulting from repetitive variationof the ignition coil ferromagnetic core between saturated andunsaturated conditions.

FIG. 12 shows the voltage across the 35 mil spark gap, located in air atatmospheric pressure, during the current discharge through this sparkgap as depicted in FIG. 11. The waveform of FIG. 12 has notch-likeportions 86 which correspond to the current spikes shown in FIG. 11,leading to strong arcs within the spark gap 26. The spark isextinguished at the point 88. Following this, a sinusoidal anddecreasing amplitude oscillation 90 take place.

FIG. 13 depicts the voltage across the capacitor C1 for two sparkdischarges corresponding to the current and voltage waveforms shown,respectively, in FIGS. 11 and 12. It may be seen that the frequency ofthis voltage across the capacitor CI for about the first 75 microsecondsoscillates at a voltage and frequency which is in excess of that whichfollows. The oscillations of voltage across the capacitor C1 during thisinitial 75 microseconds is a ferroresonant oscillation defined by theequation f V,,,/4N I The oscillations which follow also behave inaccordance with this equation, but the frequency of oscillation is thatproduced by the alternating current flowing through the second primarywinding P2. In other words, the ferroresonant oscillations lock-in atthe fixed frequency of the sustaining alternating current oscillationsin the second primary winding P2. The voltage V,,, across the capacitorC1 assumes a value defined by the foregoing equation for operation atsuch fixed frequency,

The voltage and current waveforms shown in FIG. 2 through 13 wereobtained with an ignition coil 12 having a first and second primarywindings P1 and P2 each of one turn and a secondary winding of 160turns. The primary windings P1 and P2 and the secondary winding S werewound on a ferrite (manganese zinc) core having the shape ofa closed,hollow cylinder with a central core running along its axis. The cylinderhad an outside diameter of 42 millimeters and a height of 29millimeters. The primary and secondary windings were wound about thecentral core. The capacitor C1 had a value of 500 picofarads. Theremaining components in the circuit of FIGS. 1a and lb were of thevalues indicated therein. The capacitance values are given inmicrofarads, unless otherwise specified, and the resistance values arein ohms or, as indicated, in kilohms.

The design of the saturable ferromagnetic ignition coil 12 is notcritical and may take various forms other than that described in thepreceding paragraph. Also, the value of the capacitor C1 is ofimportance in producing ferroresonance in the secondary circuit duringthe discharge of the capacitor C2 through the ignition coil primarywinding P1, but the capacitance C1 may be within a broad range. Valuesin excess of 1,000 picofarads for the capacitor C1 have been used.

The DC voltage supply for charging the capacitor C2 and the value ofthis capacitor must be sufficiently large to permit the discharge ofthis capacitor through the first primary winding P1 of the ignition coil12 to produce a ferroresonant condition, as depicted in FIGS. 7 through13, in the ignition system.

The circuitry of FIGS. la and 1b is designed to provide multiplesustained sparks during a given combustion cycle in a given combustionchamber of an engine. If it is desired to produce only one sustainedspark per combustion cycle, then the circuitry may be simplifiedconsiderably. Of course, a transistorized ignition system using a pulsegenerator driven by a distributor or the like may be used in place ofthe cam 40 and breaker points 42. Such breakerless ignition systems arewell known.

The inventors have found that the first and second primary windings P1and P2 may, if desired, be replaced by a single primary windingconnected to the SCR Q7 in the manner shown in FIG. 1a, but also havingits terminal leads connected, for example, by the leads 19 and 21 inFIG. lb, to the output of the sustain oscillator.

Based on the foregoing description of the invention, what is claimed is:

1. In combination with an internal combustion engine, a capacitordischarge ignition system, which comprises:

an ignition coil having first,and second primary windings, a secondarywinding and a ferromagnetic core about which said windings were wound;

a spark plug having electrodes spaced to form a spark gap, one of saidelectrodes being coupled to one terminal of said secondary winding;

21 first capacitor connected in series with said spark gap, one terminalof saidfirst capacitor being coupled to the other terminal of saidsecondary winding;

a second capacitor coupled to said first primary winding;

a DC source of electrical energy;

first circuit means, coupled to said second capacitor and to said firstprimary winding, for charging said second capacitor from said DC sourceof electrical energy and for discharging said second capacitor throughsaid first primary winding in timed relation to operation of saidengine;

second circuit means, coupled to said second primary winding, forproducing an oscillatory current in said second primary winding for apredetermined time interval subsequent to each discharge of said secondcapacitor through said first primary winding;

the discharge of said second capacitor through said first primarywinding and the subsequent production of said oscillatory current insaid second primary winding producing, for at least a portion of saidpredetermined time interval, a voltage in the secondary circuit ofignition coil which oscillates at a frequency defined by the expresion fV,,,/4N I where V,,, is the instantaneous maximum voltage across saidfirst capacitor, N is the number of turns in said secondary winding, andI is the magnetic flux within said secondary winding when saidferromagnetic core of said ignition coil is magnetically saturated.

. 2. An ignition system according to claim 1 where said first circuitmeans includes means for generating a gating signal for causing thedischarge of said second capacitor through said first primary windingand wherein said second circuit means includes an oscillator forgenerating an oscillatory signal and an amplifier means for amplifyingsaid oscillatory signal, said amplifier means being coupled to saidsecond primary winding to produce said oscillatory current in saidsecond primary winding, said oscillator being controlled by said gatingsignal generated by said first circuit means.

3. An ignition system according to claim 2 wherein said means forgenerating said gating signal includes a second oscillator, said secondoscillator being triggered in timed relation to operation of saidengine, said second oscillator having an output-signal from which saidgating signal is derived and which determines said predetermined timeinterval.

4. In combination with an internal combustion engine, a capacitordischarge ignition system, which comprises:

an ignition coil having first and second primary windings, a secondarywinding and a ferromagnetic core about which said windings are wound;

a spark plug having electrodes spaced to form a spark gap, one of saidelectrodes being coupled to one terminal of said secondary winding;

a first capacitor connected in series with said spark gap, one terminalof said capacitor being coupled to the other terminal of said secondarywinding;

a second capacitor coupled to said first primary winding;

a DC source of electrical energy;

first circuit means, coupled to said second capacitor and to said firstprimary winding, for charging said second capacitor from said DC sourceof electrical energy and for discharging said second capacitor throughsaid first primary winding in timed relation to operation of saidengine;

second circuit means for producing an alternating current through saidspark gap subsequent to each discharge of said second capacitor throughsaid first primary winding, said alternating current having a frequencyf defined by the expression f V,,,/4N .d where V,,, is the instantaneousmaximum voltage across said first capacitor, N, is the number of turnsin said secondary winding and I is the magnetic flux within saidsecondary winding when said ferromagnetic core of said ignition coil ismagnetically saturated.

5. An ignition system according to claim 4 wherein said second circuitmeans includes an oscillator controlled by said first circuit means,said oscillator being coupled to said second primary winding to cause anoscillatory current to flow through said second primary windingsubsequent to each discharge of said second capacitor through said firstprimary winding.

6. An ignition system according to claim 5 wherein said alternatingcurrent through said spark gap, during at least a portion of the thetime it exists, has a frequency equal to the frequency of saidoscillatory current in said second primary winding.

7. An ignition system according to claim 6 wherein said alternatingcurrent through said spark gap has a frequency greater than 17 KHZ.

8. An ignition system according to claim 6 wherein said oscillator hasan output frequency in the range from 17 to 35.7 KHZ.

9. In combination with an internal combustion engine, a capacitordischarge ignition system, which comprises:

an ignition coil having a primary winding, a secondary winding and aferromagnetic core about which said windings are wound;

a spark plug having electrodes spaced to form a spark gap, one of saidelectrodes being coupled to one terminal of said secondary winding;

a first capacitor connected in series with said spark gap, one terminalof said first capacitor being coupled to the other terminal of saidsecondary winding;

a second capacitor coupled to said primary winding;

a DC source of electrical energy;

a first circuit means, coupled to said second capacitor and to saidprimary winding, for charging said second capacitor from said DC sourceof electrical energy and for discharging said second capacitor throughsaid primary winding in timed relation to operation of said engine;

second circuit means, coupled to said primary winding, for producing anoscillatory current in said primary winding for a predetermined timeinterval subsequent to each discharge of said second capacitor throughsaid primary winding;

the discharge of said second capacitor through said primary winding andthe subsequent production of said oscillatory current in said primarywinding producing, for at least a portion of said predetermined timeinterval. a voltage in the secondary circuit of ignition coil whichoscillates at a frequency defined by the expression f V,,,/4N D,. whereV,,, is the instantaneous maximum voltage across said first capacitor,N, is the number of turns in said secondary winding, and l is themagnetic flux within said secondary winding when said ferromagnetic coreof said ignition coil is magnetically saturated.

1. In combination with an internal combustion engine, a capacitordischarge ignition system, which comprises: an ignition coil havingfirst and second primary windings, a secondary winding and aferromagnetic core about which said windings were wound; a spark plughaving electrodes spaced to form a spark gap, one of said electrodesbeing coupled to one terminal of said secondary winding; a firstcapacitor connected in series with said spark gap, one terminal of saidfirst capacitor being coupled to the other terminal of said secondarywinding; a secoNd capacitor coupled to said first primary winding; a DCsource of electrical energy; first circuit means, coupled to said secondcapacitor and to said first primary winding, for charging said secondcapacitor from said DC source of electrical energy and for dischargingsaid second capacitor through said first primary winding in timedrelation to operation of said engine; second circuit means, coupled tosaid second primary winding, for producing an oscillatory current insaid second primary winding for a predetermined time interval subsequentto each discharge of said second capacitor through said first primarywinding; the discharge of said second capacitor through said firstprimary winding and the subsequent production of said oscillatorycurrent in said second primary winding producing, for at least a portionof said predetermined time interval, a voltage in the secondary circuitof ignition coil which oscillates at a frequency defined by theexpresion f Vm/4Ns Phi s where Vm is the instantaneous maximum voltageacross said first capacitor, Ns is the number of turns in said secondarywinding, and Phi s is the magnetic flux within said secondary windingwhen said ferromagnetic core of said ignition coil is magneticallysaturated.
 2. An ignition system according to claim 1 where said firstcircuit means includes means for generating a gating signal for causingthe discharge of said second capacitor through said first primarywinding and wherein said second circuit means includes an oscillator forgenerating an oscillatory signal and an amplifier means for amplifyingsaid oscillatory signal, said amplifier means being coupled to saidsecond primary winding to produce said oscillatory current in saidsecond primary winding, said oscillator being controlled by said gatingsignal generated by said first circuit means.
 3. An ignition systemaccording to claim 2 wherein said means for generating said gatingsignal includes a second oscillator, said second oscillator beingtriggered in timed relation to operation of said engine, said secondoscillator having an output signal from which said gating signal isderived and which determines said predetermined time interval.
 4. Incombination with an internal combustion engine, a capacitor dischargeignition system, which comprises: an ignition coil having first andsecond primary windings, a secondary winding and a ferromagnetic coreabout which said windings are wound; a spark plug having electrodesspaced to form a spark gap, one of said electrodes being coupled to oneterminal of said secondary winding; a first capacitor connected inseries with said spark gap, one terminal of said capacitor being coupledto the other terminal of said secondary winding; a second capacitorcoupled to said first primary winding; a DC source of electrical energy;first circuit means, coupled to said second capacitor and to said firstprimary winding, for charging said second capacitor from said DC sourceof electrical energy and for discharging said second capacitor throughsaid first primary winding in timed relation to operation of saidengine; second circuit means for producing an alternating currentthrough said spark gap subsequent to each discharge of said secondcapacitor through said first primary winding, said alternating currenthaving a frequency f defined by the expression f Vm/4Ns Phi s where Vmis the instantaneous maximum voltage across said first capacitor, Ns isthe number of turns in said secondary winding and Phi s is the magneticflux within said secondary winding when said ferromagnetic core of saidignition coil is magnetically saturated.
 5. An ignition system accordingto claim 4 wherein said second circuit means includes an oscillatorcontrolled by said first circuit means, said oscillator being coupled tosaid second primary winding to cause an oscillatory current to flowthrough said second primary winding subsequent to each discharge of saidsecond capacitor through said first primary winding.
 6. An ignitionsystem according to claim 5 wherein said alternating current throughsaid spark gap, during at least a portion of the the time it exists, hasa frequency equal to the frequency of said oscillatory current in saidsecond primary winding.
 7. An ignition system according to claim 6wherein said alternating current through said spark gap has a frequencygreater than 17 KHz.
 8. An ignition system according to claim 6 whereinsaid oscillator has an output frequency in the range from 17 to 35.7KHz.
 9. In combination with an internal combustion engine, a capacitordischarge ignition system, which comprises: an ignition coil having aprimary winding, a secondary winding and a ferromagnetic core aboutwhich said windings are wound; a spark plug having electrodes spaced toform a spark gap, one of said electrodes being coupled to one terminalof said secondary winding; a first capacitor connected in series withsaid spark gap, one terminal of said first capacitor being coupled tothe other terminal of said secondary winding; a second capacitor coupledto said primary winding; a DC source of electrical energy; a firstcircuit means, coupled to said second capacitor and to said primarywinding, for charging said second capacitor from said DC source ofelectrical energy and for discharging said second capacitor through saidprimary winding in timed relation to operation of said engine; secondcircuit means, coupled to said primary winding, for producing anoscillatory current in said primary winding for a predetermined timeinterval subsequent to each discharge of said second capacitor throughsaid primary winding; the discharge of said second capacitor throughsaid primary winding and the subsequent production of said oscillatorycurrent in said primary winding producing, for at least a portion ofsaid predetermined time interval, a voltage in the secondary circuit ofignition coil which oscillates at a frequency defined by the expressionf Vm/4Ns Phi s where Vm is the instantaneous maximum voltage across saidfirst capacitor, Ns is the number of turns in said secondary winding,and Phi s is the magnetic flux within said secondary winding when saidferromagnetic core of said ignition coil is magnetically saturated.